//! Tracing log export into the state SQLite database.
//!
//! This module provides a `tracing_subscriber::Layer` that captures events and
//! inserts them into the dedicated `logs` SQLite database. The writer runs in a
//! background task and batches inserts to keep logging overhead low.
//!
//! ## Usage
//!
//! ```no_run
//! use codex_state::log_db;
//! use tracing_subscriber::prelude::*;
//!
//! # async fn example(state_db: std::sync::Arc<codex_state::StateRuntime>) {
//! let layer = log_db::start(state_db);
//! let _ = tracing_subscriber::registry()
//!     .with(layer)
//!     .try_init();
//! # }
//! ```

use chrono::Duration as ChronoDuration;
use chrono::Utc;
use std::sync::OnceLock;
use std::time::Duration;
use std::time::SystemTime;
use std::time::UNIX_EPOCH;

use tokio::sync::mpsc;
use tokio::sync::oneshot;
use tracing::Event;
use tracing::field::Field;
use tracing::field::Visit;
use tracing::span::Attributes;
use tracing::span::Id;
use tracing::span::Record;
use tracing_subscriber::Layer;
use tracing_subscriber::registry::LookupSpan;
use uuid::Uuid;

use crate::LogEntry;
use crate::StateRuntime;

const LOG_QUEUE_CAPACITY: usize = 512;
const LOG_BATCH_SIZE: usize = 128;
const LOG_FLUSH_INTERVAL: Duration = Duration::from_secs(2);
const LOG_RETENTION_DAYS: i64 = 10;

pub struct LogDbLayer {
    sender: mpsc::Sender<LogDbCommand>,
    process_uuid: String,
}

pub fn start(state_db: std::sync::Arc<StateRuntime>) -> LogDbLayer {
    let process_uuid = current_process_log_uuid().to_string();
    let (sender, receiver) = mpsc::channel(LOG_QUEUE_CAPACITY);
    tokio::spawn(run_inserter(std::sync::Arc::clone(&state_db), receiver));
    tokio::spawn(run_retention_cleanup(state_db));

    LogDbLayer {
        sender,
        process_uuid,
    }
}

impl Clone for LogDbLayer {
    fn clone(&self) -> Self {
        Self {
            sender: self.sender.clone(),
            process_uuid: self.process_uuid.clone(),
        }
    }
}

impl LogDbLayer {
    pub async fn flush(&self) {
        let (tx, rx) = oneshot::channel();
        if self.sender.send(LogDbCommand::Flush(tx)).await.is_ok() {
            let _ = rx.await;
        }
    }
}

impl<S> Layer<S> for LogDbLayer
where
    S: tracing::Subscriber + for<'a> LookupSpan<'a>,
{
    fn on_new_span(
        &self,
        attrs: &Attributes<'_>,
        id: &Id,
        ctx: tracing_subscriber::layer::Context<'_, S>,
    ) {
        let mut visitor = SpanFieldVisitor::default();
        attrs.record(&mut visitor);

        if let Some(span) = ctx.span(id) {
            span.extensions_mut().insert(SpanLogContext {
                thread_id: visitor.thread_id,
            });
        }
    }

    fn on_record(
        &self,
        id: &Id,
        values: &Record<'_>,
        ctx: tracing_subscriber::layer::Context<'_, S>,
    ) {
        let mut visitor = SpanFieldVisitor::default();
        values.record(&mut visitor);

        if visitor.thread_id.is_none() {
            return;
        }

        if let Some(span) = ctx.span(id) {
            let mut extensions = span.extensions_mut();
            if let Some(log_context) = extensions.get_mut::<SpanLogContext>() {
                log_context.thread_id = visitor.thread_id;
            } else {
                extensions.insert(SpanLogContext {
                    thread_id: visitor.thread_id,
                });
            }
        }
    }

    fn on_event(&self, event: &Event<'_>, ctx: tracing_subscriber::layer::Context<'_, S>) {
        let metadata = event.metadata();
        let mut visitor = MessageVisitor::default();
        event.record(&mut visitor);
        let thread_id = visitor
            .thread_id
            .clone()
            .or_else(|| event_thread_id(event, &ctx));

        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_else(|_| Duration::from_secs(0));
        let entry = LogEntry {
            ts: now.as_secs() as i64,
            ts_nanos: now.subsec_nanos() as i64,
            level: metadata.level().as_str().to_string(),
            target: metadata.target().to_string(),
            message: visitor.message,
            thread_id,
            process_uuid: Some(self.process_uuid.clone()),
            module_path: metadata.module_path().map(ToString::to_string),
            file: metadata.file().map(ToString::to_string),
            line: metadata.line().map(|line| line as i64),
        };

        let _ = self.sender.try_send(LogDbCommand::Entry(entry));
    }
}

enum LogDbCommand {
    Entry(LogEntry),
    Flush(oneshot::Sender<()>),
}

#[derive(Clone, Debug, Default)]
struct SpanLogContext {
    thread_id: Option<String>,
}

#[derive(Default)]
struct SpanFieldVisitor {
    thread_id: Option<String>,
}

impl SpanFieldVisitor {
    fn record_field(&mut self, field: &Field, value: String) {
        if field.name() == "thread_id" && self.thread_id.is_none() {
            self.thread_id = Some(value);
        }
    }
}

impl Visit for SpanFieldVisitor {
    fn record_i64(&mut self, field: &Field, value: i64) {
        self.record_field(field, value.to_string());
    }

    fn record_u64(&mut self, field: &Field, value: u64) {
        self.record_field(field, value.to_string());
    }

    fn record_bool(&mut self, field: &Field, value: bool) {
        self.record_field(field, value.to_string());
    }

    fn record_f64(&mut self, field: &Field, value: f64) {
        self.record_field(field, value.to_string());
    }

    fn record_str(&mut self, field: &Field, value: &str) {
        self.record_field(field, value.to_string());
    }

    fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
        self.record_field(field, value.to_string());
    }

    fn record_debug(&mut self, field: &Field, value: &dyn std::fmt::Debug) {
        self.record_field(field, format!("{value:?}"));
    }
}

fn event_thread_id<S>(
    event: &Event<'_>,
    ctx: &tracing_subscriber::layer::Context<'_, S>,
) -> Option<String>
where
    S: tracing::Subscriber + for<'a> LookupSpan<'a>,
{
    let mut thread_id = None;
    if let Some(scope) = ctx.event_scope(event) {
        for span in scope.from_root() {
            let extensions = span.extensions();
            if let Some(log_context) = extensions.get::<SpanLogContext>()
                && log_context.thread_id.is_some()
            {
                thread_id = log_context.thread_id.clone();
            }
        }
    }
    thread_id
}

fn current_process_log_uuid() -> &'static str {
    static PROCESS_LOG_UUID: OnceLock<String> = OnceLock::new();
    PROCESS_LOG_UUID.get_or_init(|| {
        let pid = std::process::id();
        let process_uuid = Uuid::new_v4();
        format!("pid:{pid}:{process_uuid}")
    })
}

async fn run_inserter(
    state_db: std::sync::Arc<StateRuntime>,
    mut receiver: mpsc::Receiver<LogDbCommand>,
) {
    let mut buffer = Vec::with_capacity(LOG_BATCH_SIZE);
    let mut ticker = tokio::time::interval(LOG_FLUSH_INTERVAL);
    loop {
        tokio::select! {
            maybe_command = receiver.recv() => {
                match maybe_command {
                    Some(LogDbCommand::Entry(entry)) => {
                        buffer.push(entry);
                        if buffer.len() >= LOG_BATCH_SIZE {
                            flush(&state_db, &mut buffer).await;
                        }
                    }
                    Some(LogDbCommand::Flush(reply)) => {
                        flush(&state_db, &mut buffer).await;
                        let _ = reply.send(());
                    }
                    None => {
                        flush(&state_db, &mut buffer).await;
                        break;
                    }
                }
            }
            _ = ticker.tick() => {
                flush(&state_db, &mut buffer).await;
            }
        }
    }
}

async fn flush(state_db: &std::sync::Arc<StateRuntime>, buffer: &mut Vec<LogEntry>) {
    if buffer.is_empty() {
        return;
    }
    let entries = buffer.split_off(0);
    let _ = state_db.insert_logs(entries.as_slice()).await;
}

async fn run_retention_cleanup(state_db: std::sync::Arc<StateRuntime>) {
    let Some(cutoff) = Utc::now().checked_sub_signed(ChronoDuration::days(LOG_RETENTION_DAYS))
    else {
        return;
    };
    let _ = state_db.delete_logs_before(cutoff.timestamp()).await;
}

#[derive(Default)]
struct MessageVisitor {
    message: Option<String>,
    thread_id: Option<String>,
}

impl MessageVisitor {
    fn record_field(&mut self, field: &Field, value: String) {
        if field.name() == "message" && self.message.is_none() {
            self.message = Some(value.clone());
        }
        if field.name() == "thread_id" && self.thread_id.is_none() {
            self.thread_id = Some(value);
        }
    }
}

impl Visit for MessageVisitor {
    fn record_i64(&mut self, field: &Field, value: i64) {
        self.record_field(field, value.to_string());
    }

    fn record_u64(&mut self, field: &Field, value: u64) {
        self.record_field(field, value.to_string());
    }

    fn record_bool(&mut self, field: &Field, value: bool) {
        self.record_field(field, value.to_string());
    }

    fn record_f64(&mut self, field: &Field, value: f64) {
        self.record_field(field, value.to_string());
    }

    fn record_str(&mut self, field: &Field, value: &str) {
        self.record_field(field, value.to_string());
    }

    fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
        self.record_field(field, value.to_string());
    }

    fn record_debug(&mut self, field: &Field, value: &dyn std::fmt::Debug) {
        self.record_field(field, format!("{value:?}"));
    }
}

#[cfg(test)]
mod tests {
    use std::io;
    use std::sync::Arc;
    use std::sync::Mutex;
    use std::time::Duration;

    use tokio::time::Instant;
    use tracing_subscriber::filter::Targets;
    use tracing_subscriber::fmt::writer::MakeWriter;
    use tracing_subscriber::layer::SubscriberExt;
    use tracing_subscriber::util::SubscriberInitExt;

    use super::*;

    #[derive(Clone, Default)]
    struct SharedWriter {
        bytes: Arc<Mutex<Vec<u8>>>,
    }

    impl SharedWriter {
        fn snapshot(&self) -> String {
            String::from_utf8(self.bytes.lock().expect("writer mutex poisoned").clone())
                .expect("valid utf-8")
        }
    }

    struct SharedWriterGuard {
        bytes: Arc<Mutex<Vec<u8>>>,
    }

    impl<'a> MakeWriter<'a> for SharedWriter {
        type Writer = SharedWriterGuard;

        fn make_writer(&'a self) -> Self::Writer {
            SharedWriterGuard {
                bytes: Arc::clone(&self.bytes),
            }
        }
    }

    impl io::Write for SharedWriterGuard {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.bytes
                .lock()
                .expect("writer mutex poisoned")
                .extend_from_slice(buf);
            Ok(buf.len())
        }

        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    #[tokio::test]
    async fn sqlite_feedback_logs_match_feedback_formatter_shape() {
        let codex_home =
            std::env::temp_dir().join(format!("codex-state-log-db-{}", Uuid::new_v4()));
        let runtime = StateRuntime::init(codex_home.clone(), "test-provider".to_string())
            .await
            .expect("initialize runtime");
        let writer = SharedWriter::default();

        let subscriber = tracing_subscriber::registry()
            .with(
                tracing_subscriber::fmt::layer()
                    .with_writer(writer.clone())
                    .without_time()
                    .with_ansi(false)
                    .with_target(false)
                    .with_filter(Targets::new().with_default(tracing::Level::TRACE)),
            )
            .with(
                start(runtime.clone())
                    .with_filter(Targets::new().with_default(tracing::Level::TRACE)),
            );
        let guard = subscriber.set_default();

        tracing::trace!("threadless-before");
        tracing::info_span!("feedback-thread", thread_id = "thread-1").in_scope(|| {
            tracing::info!("thread-scoped");
        });
        tracing::debug!("threadless-after");

        drop(guard);

        // SQLite exports now include timestamps, while this test writer has
        // `.without_time()`. Compare bodies after stripping the SQLite prefix.
        let feedback_logs = writer
            .snapshot()
            .replace("feedback-thread{thread_id=\"thread-1\"}: ", "");
        let strip_sqlite_timestamp = |logs: &str| {
            logs.lines()
                .map(|line| {
                    line.split_once(' ')
                        .map_or_else(|| line.to_string(), |(_, rest)| rest.to_string())
                })
                .collect::<Vec<_>>()
        };
        let feedback_lines = feedback_logs
            .lines()
            .map(ToString::to_string)
            .collect::<Vec<_>>();
        let deadline = Instant::now() + Duration::from_secs(2);
        loop {
            let sqlite_logs = String::from_utf8(
                runtime
                    .query_feedback_logs("thread-1")
                    .await
                    .expect("query feedback logs"),
            )
            .expect("valid utf-8");
            if strip_sqlite_timestamp(&sqlite_logs) == feedback_lines {
                break;
            }
            assert!(
                Instant::now() < deadline,
                "sqlite feedback logs did not match feedback formatter output before timeout\nsqlite:\n{sqlite_logs}\nfeedback:\n{feedback_logs}"
            );
            tokio::time::sleep(Duration::from_millis(10)).await;
        }

        let _ = tokio::fs::remove_dir_all(codex_home).await;
    }

    #[tokio::test]
    async fn flush_persists_logs_for_query() {
        let codex_home =
            std::env::temp_dir().join(format!("codex-state-log-db-{}", Uuid::new_v4()));
        let runtime = StateRuntime::init(codex_home.clone(), "test-provider".to_string())
            .await
            .expect("initialize runtime");
        let layer = start(runtime.clone());

        let guard = tracing_subscriber::registry()
            .with(
                layer
                    .clone()
                    .with_filter(Targets::new().with_default(tracing::Level::TRACE)),
            )
            .set_default();

        tracing::info!("buffered-log");

        layer.flush().await;
        drop(guard);

        let after_flush = runtime
            .query_logs(&crate::LogQuery::default())
            .await
            .expect("query logs after flush");
        assert_eq!(after_flush.len(), 1);
        assert_eq!(after_flush[0].message.as_deref(), Some("buffered-log"));

        let _ = tokio::fs::remove_dir_all(codex_home).await;
    }
}
